EntityType has no key defined error

问题:

Controller:

using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Web.Mvc; using MvcApplication1.Models; using System.ComponentModel.DataAnnotations.Schema;  namespace MvcApplication1.Controllers {     public class studentsController : Controller     {         //         // GET: /students/          public ActionResult details()         {             int id = 16;             studentContext std = new studentContext();            student first = std.details.Single(m => m.RollNo == id);             return View(first);         }      } } 

DbContext Model:

using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.Data.Entity;  namespace MvcApplication1.Models {     public class studentContext : DbContext     {         public DbSet details { get; set; }     } } 

Model:

using System; using System.Collections.Generic; using System.Linq; using System.Web; using System.ComponentModel.DataAnnotations.Schema;  namespace MvcApplication1.Models {     [Table("studentdetails")]     public class student     {         public int RollNo;         public string Name;         public string Stream;         public string Div;     } } 

Database table:

CREATE TABLE [dbo].[studentdetails](     [RollNo] [int] NULL,     [Name] [nvarchar](50) NULL,     [Stream] [nvarchar](50) NULL,     [Div] [nvarchar](50) NULL )   

In global.asax.cs

Database.SetInitializer(null); 

The above code lists all the classes I am working on. Upon running my application am receiving the error:

"One or more validation errors were detected during model generation" along with "Entity type has no key defined".

回答1:

The Model class should be changed to :

using System.Collections.Generic; using System.Linq; using System.Web; using System.ComponentModel.DataAnnotations.Schema; using System.ComponentModel.DataAnnotations;  namespace MvcApplication1.Models {     [Table("studentdetails")]     public class student     {         [Key]         public int RollNo { get; set; }          public string Name { get; set; }          public string Stream { get; set; }          public string Div { get; set; }     } } 

回答2:

1. Make sure public members of student class are defined as properties w/ {get; set;} (yours are public variables - a common mistake).

2. Place a [Key] annotation on top of your chosen property.

回答3:

There are several reasons this can happen. Some of these I found here, others I discovered on my own.

• If the property is named something other than Id, you need to add the [Key] attribute to it.
• The key needs to be a property, not a field.
• The key needs to be public
• The key needs to be a CLS-compliant type, meaning unsigned types like uint, ulong etc. are not allowed.
• This error can also be caused by configuration mistakes.

回答4:

i know that this post is late but this solution helped me:

    [Key]     [Column(Order = 0)]     public int RoleId { get; set; } 

added [Column(Order = 0)] after [Key] can be added by increment by 1:

    [Key]     [Column(Order = 1)]     public int RoleIdName { get; set; } 

etc...

回答5:

In my case, I was getting the error when creating an "MVC 5 Controller with view, using Entity Framework".

I just needed to Build the project after creating the Model class and didn't need to use the [Key] annotation.

回答6:

Using the [key] didn't work for me but using an id property does it. I just add this property in my class.

public int id {get; set} 

回答7:

The reason why EF framework prompt 'no key' is that EF framework needs a primary key in database. To declaratively tell EF which property the key is, you add a [Key] annotation. Or, the quickest way, add an ID property. Then, the EF framework will take ID as the primary key by default.

回答8:

All is right but in my case i have two class like this

namespace WebAPI.Model {    public class ProductsModel {          [Table("products")]         public class Products         {             [Key]             public int slno { get; set; }              public int productId { get; set; }             public string ProductName { get; set; }              public int Price { get; set; } }         }     } 

After deleting the upper class it works fine for me.

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